The cenotes are not to be missed. If you are a diver at any skill level, you would have to be crazy not to dive at least 1 cenote. 

Reef Diving 

All of the boats for reef dive leave from Playa Maya, just north of the beach town.  Every dive outfit on the beach was running people out to the reef on small boats.  Perhaps the lack of a pier or volume of divers to support big boats?  Either way, you need to be comfortable with diving off a small boat.  No dive platforms here.

Cenote Dos Ojos - SCUBA

Dos Ojos is one of the largest caverns that you can dive it.  It is approximately 15-20 minutes north of Tulum. You will need to go with a Cave Certified Diver.  The cenote has a large cave-like opening which contains a large pool or crystal clear water.  The visability in the cenote is incredible.  Everything appears to be in High Definition.  Maximum depth is 40 feet, so you can get a lot of time in.  Once you jump in you descend down and into the cave.  The formations in Dos Ojos are make up of stalagtites and stalagmites that developed before the cave was flooded.  There are many different chambers which can be explored.  Dos Ojos has a few different entries where the light peaks through. The water color changes from blue to green where the sun peaks through.

Cenote Angelita- SCUBA 

Angelita is totally unique!  It is unlike anything else.  Located a few kilos south of Tulum, it is very isolated and quiet.  The cenote is a large whole in the ground.  The diameter is probably 100' wide and it is 200' straight down.  Due to its depth, you should be an advanced diver.  The dive groups are always small.  Most dive shops will not take more than 4 people.  Entery is from the shore.

You make a quick descent to 70' in total sunlight.  The colors from above are beautiful and you can see the trees overhanging the cenote.  Below is what appeas to be a sandy bottom, with tree branches sticking up through it.  However, it is not the bottom, but a layer of sulfur, salt water and fresh water.   As you drop down a little further it appears to be more of foggy substance, rather than sand.  With the trees sticking up through, it looks like a eerie grave yard.  As you start to descend down through it you lose sight of your fins, then legs, then waist.  Crazy!  Once you are totally immersed in the sulfur layer, the visability is severely reduced.  This is where a torch comes in handy.  The sulfu later is only about 10' and below is 100% salt water.  Once below the sulfur, it is dark, but crystal clear visability has been restored.  Depth is 120'+.  In the salt water you can explore a mound that has accumulated over the years, the cenote walls, and fallen trees.  Looking up into the sulfur appears to be a 3rd dimension.  The sunlight passes through at radmon angles when the sulfur is agitated by rising bubles from your regulator.  

 The ascent up though the sulfur is also unique.  If you ascend at the same rate as your buddy, you will see his/her head emerge with the rest of his/her body hidden.  On the ascent take some time and exlore the cenote walls and take in the view from above. Simply stunning!

Overall, this is a very unique dive.  It is unlike anything you will do in the ocean or in a fresh water only quary.  Don't miss this while you are in Tulum or further north on the Mayan Riviera!

 

UPDATE:26.2.13 BY DAVID BAKER

Tulum is one of the best places anywhere to dive, to try diving or to improve your diving. There are lots of good dive shops. 

The cenote diving is unique and not to be missed. The sea diving here is good but there are better places. As well as Dos Ojos, try:

 

 • Tajma Ha - like Dos Ojos: spectacular, surprising and beautiful, also gerat for snorkelers

• Gran Cenote - ditto

• Casa Cenote - smaller and much easier to dive. Great for your first dive (ever, or as a refresher). No real overhanging caverns. Like diving in an aquarium

 

Angelita 

The description above is accurate but some poeple consider Angelita a fairly dull dive, apart from the excitement of the hydrogen sulphide cloud at 30 metres. Like all deep dives it really is best for experienced divers. You must have a torch and you must have good control over your bouyancy, so you don't end up too deep or ascending too fast. There are not many "landmarks" on the way down or up to measure yourself against. And you must have a working depth guage and SPG to keep an eye on your air.

When you pass through the cloud, visibility goes down to zero (just an eerie, white milkiness illuminated by your torch). The best way to do it is to link arms with your buddy, take a single breath before entering and exhale slowly as you pass through (it's about three metres deep). If you don't manage a single breath (I didn't) you inhale the hydrogen sulphide, which is not a problem but tastes horrible. Below the cloud you are at about 34 metres and obviously don't have much time there before you have to ascend. Being in the cloud can be disorienting and sometimes people panic, plus the entry and exit to the dive itself is slippy and difficult. It's the dive people like to say they have done but many other cenotes are much more beautiful.